Surface dyeing process for welded metal articles

ABSTRACT

A surface treatment process for a welded metal article includes following steps. Firstly, a metal article with a weld joint region is provided. Secondly, the metal article is anodized to form an anodic oxide layer on a surface thereof. Thirdly, the surface of the anodized metal article is rinsed. Fourthly, at least the anodized surface of the metal article in the region of the weld joint region is activated in a nitric acid solution. Fifthly, the anodized surface (i.e., the anodic oxide layer) of the metal article is dyed. Sixthly, the anodic oxide layer of the metal article is sealed. Finally, the metal article is rinsed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to a co-pending U.S. patent application (Attorney Docket No. US12966), entitled “SURFACE DYEING TREATMENT FOR METAL ARTICLES”, by Chih-Ben Lin et al. Such application has the same assignee as the present application and has been concurrently filed herewith. The above-identified application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to surface treatment processes and, particularly, to a surface dyeing process for a welded metal article.

2. Description of Related Art

Metal articles made of, e.g., aluminum, magnesium, titanium, or alloys thereof, possess a high quality in mechanical performance. As such, these articles have tremendous applications in many industries. The articles usually need to undergo surface treatment for improving corrosion resistance or abrasion resistance.

Anodizing is an effective surface treatment carried out in an anodizing solution for the purpose of improving the decorative quality and/or surface durability of the metal articles. During anodization of the metal articles, a porous anodic oxide film is formed over the surface of the metal articles. The anodized metal articles are often subsequently colored to obtain decorative appearances. The coloring of the metal articles can be carried out in a dye solution. An organic dye dissolved in the dye solution is introduced into pore openings of the porous anodic oxide film of the metal articles. The organic dye can be absorbed through a surface region of the porous anodic oxide film on the metal articles.

A typical metal article may be composed of two or more metal parts, which are welded together. A joint region results from the welding of the two metal parts. The joint region typically has a plurality of micro holes or slits formed therein. However, during anodizing of the metal article, a portion of the anodizing solution may penetrate into the micro holes or slits, and this penetrating portion of the solution is not easily washed out from the joint region. Dye particles can be decomposed in the anodizing solution. Thus, the organic dye cannot be absorbed through the joint region, and the joint region would be uncolored during coloring of the metal article.

Therefore, a surface treatment process for a metal article is desired, in order to overcome the above-described shortcomings.

SUMMARY OF THE INVENTION

In one embodiment thereof, a surface treatment process for a metal article is provided. In a first step of the surface treatment process, a metal article with a weld joint region is provided. In a second step of the surface treatment process, the metal article is anodized to form an anodic oxide layer on a surface thereof; the surface includes the weld joint region. In a third step of the surface treatment process, at least the anodic oxide layer of the weld joint region of the metal article is activated in a nitric acid solution. Finally, the surface of the metal article is dyed.

Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the surface treatment process for a metal article can be better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the surface treatment process for a metal article. Moreover, in the drawing, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a flow chart of a surface treatment process for a welded metal article, in accordance with a present embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a present surface treatment process for a welded metal article includes steps 10 to 80.

In step 10, a welded metal article made, e.g., of aluminum, magnesium, titanium, or alloys thereof is provided. The metal article includes at least two parts, which are joined together, for example, by plasma welding or laser welding. A weld joint region is formed between the at least two parts.

In step 20, a process for degreasing a surface of the metal article is carried out using, advantageously, an alkali-based cleaning solution so as to remove oil stains on the metal article. After being degreased, the metal article is subsequently rinsed in flowing water. It is to be understood that, additionally or alternatively, another degreasing agent such as a surfactant could be employed in step 20.

In step 30, the metal article is chemically polished in a chemical polishing solution. As part of step 30, an additional mechanical polishing component could be used, as per chemical mechanical polishing (CMP). As part of step 30, the metal article is dipped into the chemical polishing solution, which usefully contains phosphoric acid in an approximate range from 80 wt. % (percent by weight) to 90 wt. %, about 3 wt. % to 5 wt. % sulfuric acid, and about 6 wt. % to 7 wt. % nitric acid. During the chemical polishing step, a superfluous metal oxide film may be formed on the metal article, and thus a process for removing the superfluous metal oxide film may be required. The process for removing the superfluous metal oxide film can be performed by dipping the metal article into a chromic acid solution.

In step 40, an anodizing process is then performed on the surface of the metal article, and an anodic oxide layer with a plurality of fine pores therein is thereby formed on the surface of the metal article. Upon anodizing, the surface of the anodized metal article is effectively defined by the anodic oxide layer on the original metal article. The process for anodizing the metal article involves a cleaning step and an electrolysis step. The cleaning step is advantageously carried out in an alkaline solution, such as sodium hydroxide or sodium carbonate. The electrolysis step is, in one embodiment, carried out in a phosphoric acid electrolyte containing an amount in an approximate range from 0.2 wt. % to 1.0 wt. % of phosphoric acid, using the metal article as an anode. A direct current in an approximate range from 20 volts to 60 volts should be applied to the metal article. The metal article is then anodized in the electrolyte with a current density in an approximate range from 10˜50 milliamperes per square centimeter and at a temperature in an approximate range from 20° C. to 26° C., for about 20 minutes. As the electrolysis proceeds, the anodic oxide layer grows on the surface of the metal surface, with the thickness of the oxide layer increasing as the electrolysis continues (i.e., the anodizing time can be varied, in order help achieve the desired oxide layer thickness). The electrolysis step also can instead be carried out in a sulfuric acid electrolyte at a concentration in an approximate range from 100 g/l to 200 g/l. The direct current applied to the metal article is in an approximate range 8-16 volts and has a current density in an approximate range of 10˜20 milliamperes per square centimeter. During anodization of the metal article, the electrolyte (e.g., the phosphoric acid electrolyte or the sulfuric acid electrolyte) may penetrate into micro holes and/or slits in the oxide layer formed on the weld joint region.

In step 50, the anodized metal article is rinsed using a flow of water, so as to remove the electrolyte solution.

In step 60, the anodized metal article is immersed into an active solution, and the oxide layer of the weld joint region of the metal article is then activated at a temperature in an approximate range from 20° C. to 30° C. The active solution is, opportunely, a nitric acid in a concentration in an approximate range from 10 wt. % to 30 wt. %. A residual electrolyte solution, which penetrates into the micro holes and/or the micro slits of the weld joint region during the anodizing step, can be effectively displaced and thereby replaced by the nitric acid. After activation of the surface of the metal article, a rinsing process or a drying process is performed, thus removing the nitric acid from the surface and/or the weld joint region of the metal article. It is to be understood that activation is not necessarily limited to the oxide layer of the weld joint region. Instead, it is considered that activation, at a minimum, occurs in the weld joint region, as per step 60.

In step 70, the anodized metal article is immersed into a dye solution, so as to color the surface of the metal article. The dye solution contains an organic dye in a concentration in an approximate range from 1 g/l to 10 g/l. During the coloring of the metal article, dye particles in the dye solution penetrate into the pores of the anodic oxide layer of the metal article, thus coloring the surface of the anodized metal article, including the weld joint region.

In step 80, the metal article is rinsed and subsequently processed in a sealing process. The sealing process is carried out, advantageously, in a nickel salt solution, e.g. nickel acetate or nickel fluoride. The metal article is immersed in the nickel salt solution for 10 minutes to 60 minutes, with the nickel salt solution being maintained at a temperature in an approximate range from 90° C. to 96° C. The step 80, as described, yields a nickel plating. If another type/composition of protective metal plating should be desired, the metal salt(s) used in the sealing process would need to be chosen accordingly.

The sealed metal article is further rinsed via a flow of water, thus finally yielding a colored metal article with good wearability and bright luster.

It should be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A surface treatment process for a metal article, comprising the steps of: providing a metal article with a weld joint region; anodizing the metal article to form an anodic oxide layer on a surface of the metal article, the surface including the weld joint region; activating at least the anodic oxide layer of the weld joint region of the metal article, the activating being performed in a nitric acid solution; and dyeing the anodic oxide layer of the metal article.
 2. The surface treatment process as claimed in claim 1, wherein the metal article is comprised of at least one of aluminum, magnesium, and titanium.
 3. The surface treatment process as claimed in claim 1, further comprising a pretreatment process before the step of anodizing the metal article, the pretreatment process including a step of degreasing the surface of the metal article and a step of polishing the surface of the metal article.
 4. The surface treatment process as claimed in claim 3, further comprising a step of dipping the metal article in a chromic acid solution.
 5. The surface treatment process as claimed in claim 1, wherein the anodizing of the metal article involves a cleaning step and an electrolysis step, the cleaning step being carried out in an alkaline solution, the electrolysis step being carried out in an electrolyte.
 6. The surface treatment process as claimed in claim 5, wherein the electrolyte contains phosphoric acid in an approximate range from 0.2˜1.0 wt. %, using the metal article as an anode.
 7. The surface treatment process as claimed in claim 6, wherein during the electrolysis step, the metal article is anodized in the electrolyte at a current density in an approximate range from 10˜50 milliamperes per square centimeter, with a direct current in an approximate range from 20 volts to 60 volts applied thereto.
 8. The surface treatment process as claimed in claim 5, wherein the electrolyte contains sulfuric acid at a concentration in an approximate range from 100 g/l to 200 g/l.
 9. The surface treatment process as claimed in claim 6, wherein during the electrolysis step, the metal article is anodized in the electrolyte at a current density in an approximate range from 10˜20 milliamperes per square centimeter, at a temperature in an approximate range from 20° C. to 26° C.
 10. The surface treatment process as claimed in claim 1, wherein the dyeing of the anodic oxide layer of the metal article is carried out in a dye solution containing an organic dye at a concentration in an approximate range from 1 g/l to 10 g/l.
 11. The surface treatment process as claimed in claim 1, further comprising a sealing step performed after the step of dyeing the anodic oxide layer.
 12. The surface treatment process as claimed in claim 11, wherein the sealing step is carried out in a nickel salt solution.
 13. The surface treatment process as claimed in claim 1, wherein the nitric acid has a concentration in an approximate range from 10 wt. % to 30 wt. %. 